Misorientation-Controlled Cross-Plane Thermoelectricity in Twisted Bilayer Graphene

The introduction of "twist" or relative rotation between two atomically thin van der Waals membranes gives rise to periodic moiré potential, leading to a substantial alteration of the band structure of the planar assembly. While most of the recent experiments primarily focus on the electronic-band hybridization by probing in-plane transport properties, here we report out-of-plane thermoelectric measurements across the van der Waals gap in twisted bilayer graphene, which exhibits an interplay of twist-dependent interlayer electronic and phononic hybridization. We show that at large twist angles, the thermopower is entirely driven by a novel phonon-drag effect at subnanometer scale, while the electronic component of the thermopower is recovered only when the misorientation between the layers is reduced to <6°. Our experiment shows that cross-plane thermoelectricity at low angles is exceptionally sensitive to the nature of band dispersion and may provide fundamental insights into the coherence of electronic states in twisted bilayer graphene.

Interplay between spin proximity effect and charge-dependent exciton dynamics in MoSe2/CrBr3 van der Waals heterostructures

Semiconducting ferromagnet-nonmagnet interfaces in van der Waals heterostructures present a unique opportunity to investigate magnetic proximity interactions dependent upon a multitude of phenomena including valley and layer pseudospins, moiré periodicity, or exceptionally strong Coulomb binding. Here, we report a charge-state dependency of the magnetic proximity effects between MoSe2 and CrBr3 in photoluminescence, whereby the valley polarization of the MoSe2 trion state conforms closely to the local CrBr3 magnetization, while the neutral exciton state remains insensitive to the ferromagnet. We attribute this to spin-dependent interlayer charge transfer occurring on timescales between the exciton and trion radiative lifetimes. Going further, we uncover by both the magneto-optical Kerr effect and photoluminescence a domain-like spatial topography of contrasting valley polarization, which we infer to be labyrinthine or otherwise highly intricate, with features smaller than 400 nm corresponding to our optical resolution. Our findings offer a unique insight into the interplay between short-lived valley excitons and spin-dependent interlayer tunneling, while also highlighting MoSe2 as a promising candidate to optically interface with exotic spin textures in van der Waals structures.

Long-range ballistic transport of Brown-Zak fermions in graphene superlattices

In quantizing magnetic fields, graphene superlattices exhibit a complex fractal spectrum often referred to as the Hofstadter butterfly. It can be viewed as a collection of Landau levels that arise from quantization of Brown-Zak minibands recurring at rational (p/q) fractions of the magnetic flux quantum per superlattice unit cell. Here we show that, in graphene-on-boron-nitride superlattices, Brown-Zak fermions can exhibit mobilities above 10⁶ cm² V⁻¹ s⁻¹ and the mean free path exceeding several micrometers. The exceptional quality of our devices allows us to show that Brown-Zak minibands are 4q times degenerate and all the degeneracies (spin, valley and mini-valley) can be lifted by exchange interactions below 1 K. We also found negative bend resistance at 1/q fractions for electrical probes placed as far as several micrometers apart. The latter observation highlights the fact that Brown-Zak fermions are Bloch quasiparticles propagating in high fields along straight trajectories, just like electrons in zero field.

Here, the authors show that Brown-Zak fermions in graphene-on-boron-nitride superlattices exhibit mobilities above 10⁶ cm²/V s and micrometer scale ballistic transport.

Purification of human iPSC-derived cardiomyocytes by HDAC inhibition through inducing apoptosis and cell arrest in non-cardiomyocytes

Background

Cell therapy is one of the most promising strategies for treatment of heart failure. During preparation of iPSC-derived cardiomyocytes for cells therapy, it is important to eliminate the presence of residual proliferative non-target cells in the preparation as these non-target cells could present the risk of tumorgenicity. To minimize the risk, selective and more precise purification process is necessary.

Purpose

We hypothesized that the differences in proliferative activity between cardiomyocytes and non-target cells might result in different sensitivities to the drugs targeting cell growth/survival. The aim of this study is to obtain compounds that eliminate non-cardiomyocytes selectively and to study the mechanism of action of these compounds.

Methods and results

We screened 314 small compounds using both iPSCs and sorted hiPSC-derived cardiomyocytes (hiPSC-CMs). We identified several compounds, which markedly decreased the cell numbers of iPSCs, but showed minimum effects on those of hiPSC-CMs. Among them, HDAC inhibitors were selected as the most promising candidates. We examined whether HDAC inhibitors could purify hiPSC-CMs containing non-cardiomyocytes populations, which were differentiated using the classical embryoid body (EB) method. As a result, HDAC inhibitors increased the purity of cardiomyocytes (up to 98%) by decreasing non-target cells such as smooth muscle cells, endothelial cells, and endodermal lineage cells. Moreover, we confirmed HDAC inhibitors could be used for purification of cardiomyocytes in monolayer differentiation protocol using GSK3β inhibitor and Wnt inhibitor. We measured the expression levels of mRNA and protein in iPSCs and hiPSC-CMs (EB method) treated with HDAC inhibitors. mRNA levels of CDKN1A (p21) and BAX were upregulated in iPSCs. Western blotting analyses revealed that HDAC inhibitors also induced the expression of p21 and the cleavage of Caspase3 in iPSCs.

Conclusions

Our result suggests that the inhibition of HDAC enables an efficient purification of hiPSC-CMs in multiple differentiation methods. Furthermore, our data indicate that HDAC inhibitors induce the apoptosis and cell cycle arrest in iPSCs but not hiPSC-CMs.

Figure 1

Funding Acknowledgement

Type of funding source: Private company. Main funding source(s): Takeda Pharmaceutical Company Limited

Sex-related differences in clinical features and in-hospital outcomes of acute aortic dissection type b

Background

Acute aortic dissection (AAD) is a life-threatening medical condition with high morbidity and mortality. The association between female sex and poorer outcomes following surgery for AAD type A has been reported; however, the sex-related differences in clinical features and in-hospital outcomes of AAD type B remain to be elucidated.

Methods

We studied a total of 1877 patients with AAD type B who were enrolled in the Tokyo Acute Aortic Super-network from January 2013 to December 2016. Clinical features and in-hospital outcomes were compared between sexes. Independent predictors of in-hospital mortality were assessed using a multivariable analysis.

Results

The mean age of the patients was 69±13 years and 549 (29%) were females. Female patients were older than males (74±13 years vs 67±13 years; p&lt;0.001). Females had lower systolic blood pressure on admission (158±37 mmHg vs 164±38 mmHg; p=0.007) and were more likely to have altered consciousness level at presentation (8.7% vs 3.9%; p&lt;0.001), intramural hematoma (IMH)-type AAD (62.7% vs 53.6%; p&lt;0.001), and DeBakey type IIIa (28.4% vs 21.8%; p=0.002) compared with males. Females were treated with medical therapy alone more frequently (90.3% vs 85.9%; p=0.009) and had a higher in-hospital mortality rate (5.3% vs 2.6%; p=0.036). A multivariable analysis revealed that age [per year, odds ratio (OR) 1.06; 95% CI 1.04–1.09; p&lt;0.001], altered consciousness level (OR 3.28; 95% CI 1.54–6.98; p=0.002), shock/hypotension (OR 14.0; 95% CI 5.92–33.1; p&lt;0.001), classic-type AAD (OR 2.54; 95% CI 1.36–4.73; p=0.003), and medical therapy alone (OR 0.28; 95% CI 0.15–0.54; p&lt;0.001) were independent predictors of in-hospital mortality, whereas female sex was not predictive of in-hospital mortality (OR 1.64; 95% CI 0.91–2.96; p=0.10).

Conclusion

In AAD type B, females were older and had altered consciousness level, IMH-type, and a less widespread dissection more frequently than males. The overall in-hospital mortality was higher in females; however, female sex was not associated with in-hospital mortality after multivariable adjustment.

Funding Acknowledgement

Type of funding source: None

Diagnostic markers for discriminating between acute aortic dissection and acute myocardial infarction during the pre-hospital phase: analysis of 3,195 cases

 

Both acute aortic dissection (AAD) and acute myocardial infarction (AMI) present with chest pain and are life-threatening diseases that require early diagnosis and treatment for better clinical outcome. However, two critical diseases in the very acute phase are sometimes difficult to differentiate, especially prior to arrival at the hospital for urgent diagnosis and selection of specific treatment.

The aim of our study was to clarify the diagnostic markers acquired from the information gathered from medical history taking and physical examination for discriminating AAD from AMI by using data from the Tokyo Cardiovascular Care Unit (CCU) Network database.

We examined the clinical features and laboratory data of patients with AAD and AMI who were admitted to the hospital in Tokyo between January 2013 and December 2015 by using the Tokyo CCU Network database. The Tokyo CCU Network consists of &gt;60 hospitals that fulfil certain clinical criteria and receive patients from ambulance units coordinated by the Tokyo Fire Department. Of 15,061 patients diagnosed as having AAD and AMI, 3,195 with chest pain within 2 hours after symptom onset (537 AAD and 2,658 AMI) were examined. The patients with out-of-hospital cardiac arrest were excluded.

We compared the clinical data of the patients with chest pain who were diagnosed as having AAD and AMI. The following indicators were more frequent or had higher values among those with AAD: female sex (38% vs. 20%, P&lt;0.001), systolic blood pressures (SBPs) at the time of first contact by the emergency crew (142 mmHg vs. 127 mmHg), back pain in addition to chest pain (54% vs. 5%, P&lt;0.001), history of hypertension (73% vs. 58%, P&lt;0.001), SBP ≥150 mmHg (39% vs. 22%, P&lt;0.001), back pain combined with SBP ≥150 mmHg (23% vs. 0.8%, P&lt;0.001), and back pain with SBP &lt;90 mmHg (4.5% vs. 0.1%, P&lt;0.001). The following data were less frequently observed among those with AAD: diabetes mellitus (7% vs. 28%, P&lt;0.001), dyslipidaemia (17% vs. 42%, P&lt;0.001), and history of smoking (48% vs. 61%, P&lt;0.001). The multivariate regression analysis suggested that back pain with SBP ≥150 mmHg (odds ratio [OR] 47; 95% confidence interval [CI] 28–77; P&lt;0.001), back pain with SBP &lt;90 mmHg (OR 68, 95% CI 16–297, P&lt;0.001), and history of smoking (OR 0.49, 95% CI 0.38–0.63, P&lt;0.001) were the independent markers of AAD. The sensitivity and specificity of back pain with SBPs of ≥150 mmHg and back pain with SBPs &lt;90 mmHg for detecting AAD were 23% and 99%, and 4% and 99%, respectively.

In patients with chest pain suspicious of AAD and AMI, “back pain accompanied by chest pain with SBP ≥150 mmHg” or “back pain accompanied by chest pain with SBP &lt;90 mmH” is a reliable diagnostic marker of AAD with high specificity, although the sensitivity was low. The two SBP values with back pain are markers that may be useful for the ambulance crew at their first contact with patients with chest pain.

Funding Acknowledgement

Type of funding source: None

A comparison of rate control and rhythm control in tachycardia induced cardiomyopathy patients with persistent atrial flutter

Background/Introduction

Tachycardia induced cardiomyopathy (TIC) is a potentially reversible dysfunction of the left ventricle (LV) caused by tachyarrhythmias. Early recognition of TIC and treatment of the culprit arrhythmia using pharmacological therapy or catheter ablation results in the recovery of LV function. For atrial flutter (AFL)-induced TIC, rhythm control strategy, such as catheter ablation has been recommended. On the other hand, the efficacy of rate control strategy has remained unclear due to the difficulty of control with arrhythmic medications. However, not all patients can take rhythm control treatments due to their backgrounds.

Purpose

The aim of this cohort study was to establish whether rate control strategy using β-blocker is as effective as invasive rhythm control strategy for the recovery of LV function in patients with TIC due to AFL.

Methods

We prospectively assessed 47 symptomatic non-ischaemic heart failure (HF) patients with left ventricular ejection fraction (LVEF) below 50% and suspected TIC induced by persistent AFL. Patients were divided into rhythm control strategy group (n=22, treatment: catheter ablation, electrical cardioversion) and rate control strategy group (n=25, treatment: bisoprolol). As a sub-group study, the rate control strategy group was divided into the strict rate control group (n=12, average heart rate below 80 bpm) and lenient rate control group (n=13, average heart rate below 110 bpm). The primary outcome was the recovery of LV function, defined as an increase of LVEF over 20% or to a value of 55% or greater after 6 months.

Results

There were no significant differences in baseline AFL heart rate, New York Heart Association class, LVEF, estimated glomerular filtration rate, and brain natriuretic peptide between the two groups. A greater proportion of patients who showed the recovery of LVEF after 6 months belonged to the rhythm control strategy group (90.9% vs. 52.0%, p=0.004). The cumulative incidence of HF re-hospitalization was significantly higher in the rate control strategy group than in the rhythm control strategy group (hazard ratio: 4.90, 95% CI: 1.06–22.69). As a result of sub-group study, LVEF recovery was greater in the strict rate control group compared to the lenient rate control group (75.0% vs. 30.8%, p=0.027)

Conclusion

Rate control strategy was significantly inferior to rhythm control strategy for the recovery of LVEF in TIC patients with persistent AFL. Rhythm control should be the first choice in the management of TIC with AFL, and strict rate control should be an alternative if rhythm control is not available.

Primary outcomes

Funding Acknowledgement

Type of funding source: None

Electron-Hole Crossover in Gate-Controlled Bilayer Graphene Quantum Dots

Electron and hole Bloch states in bilayer graphene exhibit topological orbital magnetic moments with opposite signs, which allows for tunable valley-polarization in an out-of-plane magnetic field. This property makes electron and hole quantum dots (QDs) in bilayer graphene interesting for valley and spin-valley qubits. Here, we show measurements of the electron-hole crossover in a bilayer graphene QD, demonstrating opposite signs of the magnetic moments associated with the Berry curvature. Using three layers of top gates, we independently control the tunneling barriers while tuning the occupation from the few-hole regime to the few-electron regime, crossing the displacement-field-controlled band gap. The band gap is around 25 meV, while the charging energies of the electron and hole dots are between 3 and 5 meV. The extracted valley g-factor is around 17 and leads to opposite valley polarization for electrons and holes at moderate B-fields. Our measurements agree well with tight-binding calculations for our device.

Isolated Superior Mesenteric Artery Dissection Mimicking Impending Rupture of Abdominal Aortic Aneurysm

Patient: Male, 66-year-old

Final Diagnosis: Isolated superior mesenteric artery dissection

Symptoms: Abdominal and back pain

Medication:—

Clinical Procedure: —

Specialty: Surgery

Neutral and charged dark excitons in monolayer WS2

Low temperature and polarization resolved magneto-photoluminescence experiments are used to investigate the properties of dark excitons and dark trions in a monolayer of WS2 encapsulated in hexagonal BN (hBN). We find that this system is an n-type doped semiconductor and that dark trions dominate the emission spectrum. In line with previous studies on WSe2, we identify the Coulomb exchange interaction coupled neutral dark and grey excitons through their polarization properties, while an analogous effect is not observed for dark trions. Applying the magnetic field in both perpendicular and parallel configurations with respect to the monolayer plane, we determine the g-factor of dark trions to be g ∼ -8.6. Their decay rate is close to 0.5 ns, more than 2 orders of magnitude longer than that of bright excitons.

Effects of royal jelly on bone metabolism in postmenopausal women: a randomized, controlled study

OBJECTIVES

This study aimed to evaluate the effects of royal jelly (RJ) supplementation on bone metabolism in postmenopausal women.

METHODS

This was a randomized, double-blind, placebo-controlled clinical trial. Seventy-two healthy postmenopausal women aged 45-60 years within 5 years after menopause were randomized into two groups: women in the RJ group (n = 36) received capsules containing dried RJ (equivalent to 3000 mg of fresh RJ); and women in the placebo group (n = 36) received placebo daily for 6 months. Bone mineral density (BMD) of the lumbar spine (L2-L4) and left proximal femur, hip structural analysis (HSA) of the left hip, and bone turnover markers were measured.

RESULTS

Although women in the placebo group experienced a significant loss of BMD and deterioration in HSA parameters of the femur, no significant differences were found in these parameters in women in the RJ group. The levels of total procollagen type 1 N-terminal propeptide (P1NP) and tartrate-resistant acid phosphatase decreased significantly in the placebo group; however, the total P1NP level, a marker of bone formation, was not significantly different in the RJ group at postintervention compared with baseline.

CONCLUSION

RJ consumption may ameliorate decreases in femoral BMD and strength in postmenopausal women.

Highly energy-tunable quantum light from moiré-trapped excitons

Photon antibunching, a hallmark of quantum light, has been observed in the correlations of light from isolated atomic and atomic-like solid-state systems. Two-dimensional semiconductor heterostructures offer a unique method to create a quantum light source: Moiré trapping potentials for excitons are predicted to create arrays of quantum emitters. While signatures of moiré-trapped excitons have been observed, their quantum nature has yet to be confirmed. Here, we report photon antibunching from single moiré-trapped interlayer excitons in a heterobilayer. Via magneto-optical spectroscopy, we demonstrate that the discrete anharmonic spectra arise from bound band-edge electron-hole pairs trapped in moiré potentials. Last, we exploit the large permanent dipole of interlayer excitons to achieve large direct current (DC) Stark tuning up to 40 meV. Our results confirm the quantum nature of moiré-confined excitons and open opportunities to investigate their inhomogeneity and interactions between the emitters or energetically tune single emitters into resonance with cavity modes.

Relationship between Histological Grade and Histopathological Appearance in Canine Mammary Carcinomas

Canine mammary carcinomas are common tumours in female dogs and histopathological examination has an important role in identifying whether they are benign or malignant. The latest and most commonly used histological grading system was established by Peña et al. (2013) and is based on the extent of tubule formation, nuclear pleomorphism and number of mitoses. Before the establishment of this grading system, tumour size and classical histological indicators of malignancy such as lymphovascular invasion, infiltration into surrounding tissue, necrosis and presence of a micropapillary pattern were important predictors of biological behaviour. However, the system of Peña et al. does not consider tumour size or these histological features. Clarifying the association of these features and histological grade, especially in grade II and III carcinomas, is important. In this study, we confirmed that the system of Peña et al. is effective for predicting biological behaviour and that evaluation of histological features of malignancy reinforced histological grade, as determined by the system of Peña et al., especially in grade II carcinomas.

Measurement of the spin-forbidden dark excitons in MoS2 and MoSe2 monolayers

Excitons with binding energies of a few hundreds of meV control the optical properties of transition metal dichalcogenide monolayers. Knowledge of the fine structure of these excitons is therefore essential to understand the optoelectronic properties of these 2D materials. Here we measure the exciton fine structure of MoS2 and MoSe2 monolayers encapsulated in boron nitride by magneto-photoluminescence spectroscopy in magnetic fields up to 30 T. The experiments performed in transverse magnetic field reveal a brightening of the spin-forbidden dark excitons in MoS2 monolayer: we find that the dark excitons appear at 14 meV below the bright ones. Measurements performed in tilted magnetic field provide a conceivable description of the neutral exciton fine structure. The experimental results are in agreement with a model taking into account the effect of the exchange interaction on both the bright and dark exciton states as well as the interaction with the magnetic field.

Erratum: Evolution of π^{0} Suppression in Au+Au Collisions from sqrt[s_{NN}]=39 to 200 GeV [Phys. Rev. Lett. 109, 152301 (2012)]

This corrects the article DOI: 10.1103/PhysRevLett.109.152301.

Demonstration of a polariton step potential by local variation of light-matter coupling in a van-der-Waals heterostructure

The large oscillator strength of excitons in transition metal dichalcogenide layers facilitates the formation of exciton-polariton resonances for monolayers and van-der-Waals heterostructures embedded in optical microcavities. Here, we show, that locally changing the number of layers in a WSe₂/hBN/WSe₂ van-der-Waals heterostructure embedded in a monolithic, high-quality-factor cavity gives rise to a local variation of the coupling strength. This effect yields a polaritonic stair case potential, which we demonstrate at room temperature. Our result paves the way towards engineering local polaritonic potentials at length scales down to atomically sharp interfaces, based on purely modifying its real part contribution via the coherent light-matter coupling strength g.

Cascade of phase transitions and Dirac revivals in magic-angle graphene

Twisted bilayer graphene near the magic angle^1-4 exhibits rich electron-correlation physics, displaying insulating^3-6, magnetic^7,8 and superconducting phases^4-6. The electronic bands of this system were predicted^1,2 to narrow markedly^9,10 near the magic angle, leading to a variety of possible symmetry-breaking ground states^11-17. Here, using measurements of the local electronic compressibility, we show that these correlated phases originate from a high-energy state with an unusual sequence of band population. As carriers are added to the system, the four electronic 'flavours', which correspond to the spin and valley degrees of freedom, are not filled equally. Rather, they are populated through a sequence of sharp phase transitions, which appear as strong asymmetric jumps of the electronic compressibility near integer fillings of the moiré lattice. At each transition, a single spin/valley flavour takes all the carriers from its partially filled peers, 'resetting' them to the vicinity of the charge neutrality point. As a result, the Dirac-like character observed near charge neutrality reappears after each integer filling. Measurement of the in-plane magnetic field dependence of the chemical potential near filling factor one reveals a large spontaneous magnetization, further substantiating this picture of a cascade of symmetry breaking. The sequence of phase transitions and Dirac revivals is observed at temperatures well above the onset of the superconducting and correlated insulating states. This indicates that the state that we report here, with its strongly broken electronic flavour symmetry and revived Dirac-like electronic character, is important in the physics of magic-angle graphene, forming the parent state out of which the more fragile superconducting and correlated insulating ground states emerge.

Observation of the Spin-Orbit Gap in Bilayer Graphene by One-Dimensional Ballistic Transport

We report on measurements of quantized conductance in gate-defined quantum point contacts in bilayer graphene that allow the observation of subband splittings due to spin-orbit coupling. The size of this splitting can be tuned from 40 to 80  μeV by the displacement field. We assign this gate-tunable subband splitting to a gap induced by spin-orbit coupling of Kane-Mele type, enhanced by proximity effects due to the substrate. We show that this spin-orbit coupling gives rise to a complex pattern in low perpendicular magnetic fields, increasing the Zeeman splitting in one valley and suppressing it in the other one. In addition, we observe a spin polarized channel of 6e^{2}/h at high in-plane magnetic field and signatures of interaction effects at the crossings of spin-split subbands of opposite spins at finite magnetic field.

Minibands in twisted bilayer graphene probed by magnetic focusing

Magnetic fields force ballistic electrons injected from a narrow contact to move along skipping orbits and form caustics. This leads to pronounced resistance peaks at nearby voltage probes as electrons are effectively focused inside them, a phenomenon known as magnetic focusing. This can be used not only for the demonstration of ballistic transport but also to study the electronic structure of metals. Here, we use magnetic focusing to probe narrowbands in graphene bilayers twisted at ~2°. Their minibands are found to support long-range ballistic transport limited at low temperatures by intrinsic electron-electron scattering. A voltage bias between the layers causes strong minivalley splitting and allows selective focusing for different minivalleys, which is of interest for using this degree of freedom in frequently discussed valleytronics.

Localized Nanoresonator Mode in Plasmonic Microcavities

Submicron-thick hexagonal boron nitride crystals embedded in noble metals form planar Fabry-Perot half-microcavities. Depositing Au nanoparticles on top of these microcavities forms previously unidentified angle- and polarization-sensitive nanoresonator modes that are tightly laterally confined by the nanoparticle. Comparing dark-field scattering with reflection spectroscopies shows plasmonic and Fabry-Perot-like enhancements magnify subtle interference contributions, which lead to unexpected redshifts in the dark-field spectra, explained by the presence of these new modes.

Ultra-long carrier lifetime in neutral graphene-hBN van der Waals heterostructures under mid-infrared illumination

Graphene/hBN heterostructures are promising active materials for devices in the THz domain, such as emitters and photodetectors based on interband transitions. Their performance requires long carrier lifetimes. However, carrier recombination processes in graphene possess sub-picosecond characteristic times for large non-equilibrium carrier densities at high energy. An additional channel has been recently demonstrated in graphene/hBN heterostructures by emission of hBN hyperbolic phonon polaritons (HPhP) with picosecond decay time. Here, we report on carrier lifetimes in graphene/hBN Zener-Klein transistors of ~30 ps for photoexcited carriers at low density and energy, using mid-infrared photoconductivity measurements. We further demonstrate the switching of carrier lifetime from ~30 ps (attributed to interband Auger) down to a few picoseconds upon ignition of HPhP relaxation at finite bias and/or with infrared excitation power. Our study opens interesting perspectives to exploit graphene/hBN heterostructures for THz lasing and highly sensitive THz photodetection as well as for phonon polariton optics.

Long carrier lifetimes are beneficial for graphene-based optoelectronics, but carrier recombination processes in graphene possess sub-picosecond characteristic times. Here, the authors report carrier lifetimes ~30 ps at low energy in graphene/hBN Zener-Klein transistors, attributed to interband Auger processes.